The constant decrease and loss of the forest cover and environmental contamination has triggered the development of technologies that impede deforestation, which is why—currently—different processes have been developed for the treatment of agricultural wastes from the sugarcane harvest. At industrial level, we find that processes of transformation of the plant material to obtain paper historically represent the longest experience in managing lignocellulosic materials, which is why the paper industry has been in charge of setting the pace in the design of processes to extract and separate cellulose from the complex formed with lignin and hemicellulose. This industry has been using an important quantity of chemical and enzymatic processes to treat the material, which in some cases are responsible for generating organo-chlorine compounds that negatively affect the environment (Eriksson K. E. 1990. Biotechnolgy in the pulp and paper industry. Wood Sci. Technol., 24: 79-101).
Traditionally, paper is produced by pulping a material that contains cellulosic fibers, interweaving the cellulosic fibers to form a humid network, and drying of the humid network. Pulping can be carried out through different methodologies, while the most common source of cellulosic fiber used in the processes is wood pulp from trees, other fibrous plant materials are also used like cotton, hemp plant, flax, rice, sugarcane, bagasse, straw, and bamboo, among others. Particularly, sugarcane bagasse is composed of three polymeric-type essential ingredients: cellulose at 40 to 45%, hemi-cellulose (xylan) at 28 to 30%, and lignin at 19 to 21%, in addition to other substances and to the cell mass.
The use of wastes from the sugarcane harvest result especially interesting for the pulping industry, given that sugarcane presents high contents of cellulosic-type fibrous materials like cellulose, hemicellulose, and lignin used for paper production and in a broad variety of industrial and consumer products.
In the state of the technique, it is acknowledged that fractioning of polymeric components from plant biomass represents an obstacle for the industry, which is why research related to delignifying different lignocellulosic materials has been of interest over the last two decades (Hendrinks A. T. W. M. and Zeeman G., 2009. Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresource technology. 100:10-18; Demirbas A., 2007. Progress and recent trends in biofuels. Progress in energy and combustion science. 33:1-18; Knauf M., Moniruzzaman M., 2004. Ligno-cellulosic biomass processing: A perspective. International sugar journal. 106:147-150) to the point that different stages have been created within the processes known for the treatment of plant material and, in other cases, novel processes have been designed by applying advanced technologies to obtain cellulosic and hemicellulosic fibers as raw material for the paper industry. Regarding pretreatments, chemical processes, biological processes, and to a lesser degree enzymatic processes have been studied, as well as pretreatment with ionizing radiation.
Some of the investigations related to treatment of sugarcane bagasse and leaves subjected to different pretreatments were published by Gonçalves et al., (Gonçalves A. R., Benar P., Costa S. M., Ruzene D. S., Moriya R. Y., Luz S. M., Ferreti P., 2005. Integrated processes for use of pulps and lignins obtained from sugarcane bagasse and straw. Applied Biochemistry and Biotechnology. Vol 121-124: 821-826). In their investigation different alternatives were suggested for use of wastes and they reported on the composition of sugarcane bagasse, indicating that it contains 43.7% cellulose, 24.4% hemicellulose, 28% lignin, and 0.75% ash. However, their studies do not contribute to the state-of-the-art on the composition of sugarcane leaves as starting material for pulp production or as precursor to obtain paper.
Also, García and Larrahondo studied the chemical hydrolysis of wastes from the sugarcane harvest, particularly, leaves and buds through using sulfuric acid diluted in concentrations ranging between 5, 10, 15, 20, and 30% v/v, conserving the temperature range between 97 and 107° C., for an approximate reaction time of 6.5 hours. The study analyzed the liberation of glucose during each hour and all the findings reported bear in mind the prior separation of the sugarcane leaves and buds.
Traditionally, sugarcane leaves and buds are burnt before the start of the harvest, and in those cases in which green cut is carried out, the plant material is abandoned on the field to allow for its decomposing.
According to data reported (Torres J. S. y Villegas F., 2006. Manejo y aprovechamiento de residuos de la cosecha en verde. Serie técnica No 35 (Cenicaña). Marzo de 2006), it is estimated that after the sugarcane green harvest 50 to 70 t/ha of green biomass are produced and if it is considered that in 15-month cycles the contribution of wastes in cultivated areas is mainly constituted by the buds and portions adhered to the stalk like green and dry leaves, making it necessary to develop a process that permits its utilization and, thus, contribute to decrease environmental contamination. This contribution of biomass becomes an important reserve of organic matter for the system of sustainable production from the sugarcane crop, while promoting the recycling of the plant material for other derived industries like paper production.
It is known that fiber from buds and from leaves differs morphologically; the latter constitute 20% of the plant and may be considered long fibers, considering them a suitable material to substitute soft wood fibers.
The energy supply from sugar mills from sugarcane bagasse brings to another scenario where it is imperative and necessary to develop other alternative sources of fiber that permit a stable supply to the industry and substitution of imports. Leaves and buds emerge as an alternative source of promising fiber in our country for the cellulose and paper industry in years to come.
Using bagasse from sugarcane and eucalyptus for paper production is still in doubt, although it is currently constituted as the main fibrous source for the cellulose industry and for production of paper and agglomerates in Colombia, the requirements of the digestion process of sugarcane bagasse and subsequent fractioning of the fibers for paper production and the improper exploitation of lumber have placed at environmental risk the zones where both the treatment and exploitation take place, which is why obtaining pastes from lignocellulosic wastes provided by wastes from sugarcane green harvest like leaves and buds, offers the possibility of creating technological alternatives based on the treatment of substitute materials and products derived from sugarcane cultivation with higher added value, lower consumption of energy required for transformation, along with the possibility to obtain paper and raw material more economically.
Also, with respect to patent publications related to the use of lignocellulosic material to manufacture paper, there is document WO 2010060183, which discloses a modular process of bio-refinement to separate and process lignocellulosic material comprising the classification and fractioning of lignocellulosic material by reaction with aliphatic alcohol or with acetone, to obtain a solid cellulosic fraction (VHMW). Delignifying of the VHMW fraction is conducted in the presence of ClO2 at concentrations ranging between 3 and 4% and a temperature between 60 and 80° C., followed by washing with water and then, washing with diluted alkaline solution at a temperature between 45 and 90° C. The fractions obtained contain derivatives of high and medium molecular weight lignin (HMW-MMW) and very low molecular weight lignin (VLMW). Finally, in an anaerobic digestion module the semi-solid waste is processed with a biogas and a liquid effluent.
Likewise, patent EP0716182 discloses a method for delignifying and bleaching pulp comprising the formation of a pulp by pulping with organic solvents (Kappa number between 20 and 70), from fibrous plant material, washed with a solution that contains aliphatic alcohol at a concentration of 20 to 80% v/v and then, washed with water. Thereafter, the pulp is bleached by treating with peroxide at a concentration of 0.2 to 2% w/w, washed and delignified by treating with sodium hydroxide (NaOH) at a concentration of 2 to 8% w/w and pressure between 30 and 100 psig. Thereafter, bleaching is carried out with peroxide in the presence of a chelating transition metal added at a concentration between 0.05 to 1% and finally, washing of the pulp is done with sulfurous acid at pH 2-3. Optionally, ozone treatment is included.
U.S. Pat. No. 4,956,048 refers to a method to improve the pulping and chemical bleaching that includes repeated washing of the pulp with water and pretreatment of the material with a hydro-alcoholic mixture and de-ionized water, to continue with the bleaching stage; thus, accomplishing the reduction of the formation of chlorinated dioxins and furans.
Likewise, U.S. Pat. No. 5,531,865 discloses a process to prepare cellulose for human consumption comprising the reduction of the plant material's particle size (20 mesh), removal of lipid compounds, dissolution in water, and cooking with gaseous Cl to obtain a pulp that is re-dispersed in water and oxidized in the presence of chlorine. Then, the free Cl is removed and NaOH is added to digest the cellulosic material present; the pulp is separated and the oxidation stage is repeated.
It is notable that in recent years, great interest has been generated in the search for new alternatives for processes of obtaining cellulosic pulp, seeking to improve those already existing and trying to create new methods.
Practically all the laboratories of the big cellulose and paper manufacturers are dedicated to evaluating their production processes attempting to not only modify, but substitute the conventional production systems and the process developed constitutes a technological alternative for the industry because it reduces production costs based on detailed knowledge of the kinetics of the delignifying process, which also provides information on the probable energy consumption of this chemical reaction stage.
The invention process is mainly characterized by presenting a first stage of cooking the lignocellulosic material to dissolve the lignin and other non-cellulosic portions of the material that permits forming a pulp of individual fibers that can again be joined, forming a paper sheet.
The advantages associated to one of the modalities of the invention basically consist of using ethanol to obtain pulp and combine it with alkaline processes, increasing the selectivity of delignifying and leaving the hemicellulose almost intact because of the addition of alcohols and amines during the production of alkaline pulps.
In this order, a method needs to be designed to process plant material from sugarcane harvest wastes that will overcome the disadvantages associated to temperature and to pulping time and which will permit controlling the advance of delignifying through indicators like the H factor. All this, bearing in mind that no industrial process exists that functions solely on a two-stage alcohol-water process and subsequent soft delignifying with ethanol chlorine dioxide and which also uses a mixture of sodium hydroxide and potassium hydroxide as catalyst and which overcomes the disadvantages of the methods traditionally used, where there are higher costs in required infrastructure because these require recovery boilers and longer cooking times, as well as higher temperature and concentration of solvents.